This study will determine the effect of recombinant human interleukin 12 (rhIL-12)on HIV-infected subjects with CD4<50 who have no evidence of serious ongoing opportunistic infections but are at risk for AIDS-related disseminated Mycobacterium avium complex (MAC) infection. It will determine the tolerance of a range of chronic subcutaneous rhIL-12 dosing regimens, and characterize their immunologic, antiviral, and potential antimycobacterial effects. In addition, based on MTD of rhIL-12 tolerated by subjects with <50 CD4+ T cells/ml (Part A), a second group of subjects with 300-500 CD4+ T cells/ml will receive the MTD of the rhIL-12 or matching placebo to validate the reliability of the functional immunological evaluations and assess the in vivo immunologic activity of rhIL-12 in these subjects, who are not profoundly immunosuppressed.